<p dir="ltr">Applications of Lithium-ion batteries (LIBs) are so widely spread from transportation like electric vehicles to portable storage devices. This is mainly due to their lighter weight and smaller size with higher energy density when compared to Lead-acid, Nickel Cadmium (Ni-Cd), and other batteries. One of the applications of LIB includes electric propulsion in-air like quadcopters. These electrically-propelled vehicles have diverse applications including risky jobs like wildlife management, search and rescue, and jobs that can be automated such as delivery of smaller packages, urban planning, and so on. These electrically-propelled vehicles produce heat around the LIB which leads to thermal abuse of the battery. Also, there are often cases where LIB undergoes different abuse conditions in-air when operating these vehicles. Present battery BMSs are highly accurate but require edge and cloud with a deep learning model to safely operate quadcopters in the air. In the work, we present a BMS capable of edge-cloud data transfer with a deep-learning model to predict the RUL of the battery. Benchmark differences between data collected on-ground and in-air are presented for comparison. It turns out that the temperature collected in the air is less than the temperature on the ground when different current profiles are experimented on different batteries used in quadcopters. This study helps in the improvement of BMS with edge-cloud and deep-learning models and helps in understanding the behavior of battery in-air.</p>

<p dir="ltr">Carbon-Carbon (C/C) composites have been shown to be a preferred material for high temperature applications as they retain their properties and performance at temperatures in excess of 2000°C. This study shows that High Temperature Treatment (HTT) at 2400°C for 4 hrs followed by two subsequent Polymer Infiltration and Pyrolysis (PIP) cycles using SC1008 phenolic resin changes the failure mechanism of 2D C/C which has been subject to directional ablation prior to flexural testing. The study observes that prior directional ablation of the non-HTT C/C condition decreases flexural strength by 50.2%, whereas negligible change for the HTT C/C condition was observed (6.6%). This is attributed to the significant degradation of the tensile surface of the non-HTT C/C during ablation corresponding to an average linear thickness loss of 0.321mm (Std Dev = 0.223mm) and average mass loss of 0.364g (Std Dev = 0.196g) while the HTT recorded 0.033mm (Std Dev = 0.005mm) and 0.032g (Std Dev = 0.008g) respectively. The difference in degradation is attributed to the microstructure which was characterised through X-Ray Diffraction and Scanning Electron Microscopy. It is shown that HTT transformed the carbon matrix from a glassy/amorphous matrix to a layered matrix with an indicative increased degree of graphitisation (from 0.52 to 0.69). This not only increased the average density from 1.511 g/cm³ (Std Dev = 0.002 g/cm³) to 1.652 g/cm³ (Std Dev = 0.003 g/cm³) but also increased the average thermal conductivity from 9.1 W/mK (Std Dev = 1.06 W/mK) to 13.3 W/mK (Std Dev = 1.32 W/mK). This ultimately contributed to a reduction in available sites for the oxidation reaction to occur, while also allowing for thermal energy to be conducted away from the ablation surface reducing the amount of heat related damage. For conditions without and with prior ablation damage, the non-HTT C/C is found to fail in matrix dominated tension with the fibres and matrix breaking in a single plane originating at the tensile surface and propagating towards the neutral axis whereas the HTT C/C is found to fail in shear at the neutral axis with the fibres-matrix debonding being the primary failure mechanism. The non-HTT C/C is found to have an average flexural strength of 88.8 MPa (Std Dev = 13.7 MPa) and flexural modulus 81.0 GPa (Std Dev = 10.5 GPa), where the HTT C/C has 196.7 MPa (Std Dev = 31.4 MPa) and 115.2 GPa (Std Dev = 3.3 GPa) respectively. Lastly, this study found that a square notch in the non-HTT C/C condition resulted in a 23.9% and 26.4% reduction in flexural strength for conditions without and with prior ablation damage, respectively. No change in the failure mechanism was observed for notched specimens compared to un-notched specimens, and the debit in strength was attributed to broken fibers created by the notch.</p>

<p dir="ltr">In composites manufacturing, predicting the shape change in parts is vital for making sure part dimensions are properly compensated. Different factors in the manufacturing process, such as the temperature change throughout a thermoset cure cycle, can influence shape change. The compensation process becomes more difficult for geometries with double curvature, as interactions between the two radii of curvature can reduce the effectiveness of applying methodologies for single curvature geometries. Additionally, using finite element analysis (FEA) to predict shape change can be costly and time-consuming depending on part geometry.</p><p dir="ltr">This thesis studies an approach for predicting the shape change of a symmetric thermoset laminate with a double-curved L-angle section in its geometry. Specifically, the conservation of Gaussian curvature is applied to predict shape change. The geometry studied in this thesis can be broken down and analyzed as a segment of a torus, which is attached on one end by a cylinder and on the other end by a curved flange. Varying the length of the cylinder and flange sections, the effectiveness of Gauss’s theorem is determined for the different part geometries, with developed formulas compared against finite element simulations and experimental measurements.</p><p dir="ltr">By approximating torus segments with certain geometric criteria as cylinders, linear elasticity equations for a cylinder undergoing free thermal strain can be solved and the change in the larger arc length in the double-curved geometry is predicted after deformation. The integral form of Gauss’ theorem is then applied to determine the deformed angle of the larger arc, from which geometric relations can be applied to extract the deformed radius. Abaqus is used first to study the torus segment on its own, and then to see the effects of the cylinder and flange segments on the overall geometry. Experimental measurements are also used as a comparison.</p><p dir="ltr">Generally, the formula derived using Gauss’ theorem predicts shape change very well for the torus segment on its own. When cylinder and flange segments are included in the geometry, an empirical correction factor can be introduced to account for geometrically induced stiffening effects. Future developments and next steps in this research are discussed.</p>

<div> <p>Fiber reinforced polymer composites are widely used in manufacturing advanced light weight structures for the aerospace, automotive, and energy sectors owing to their superior stiffness and strength. With the increasing use of composites, there is an increasing need to monitor the health of these structures during their lifetime. Currently, health monitoring in filament wound composites is facilitated by embedding piezoelectrics and optical fibers in the composite during the manufacturing process. However, the incorporation of these sensing elements introduces sites of stress concentration which could lead to progressive damage accumulation. In addition to introducing weak spots in the structure, they also make the manufacturing procedure difficult. </p> <p> </p> <p>Alternatively, nanofiller modification of the matrix imparts conductivity which can be leveraged for real time health monitoring with fewer changes to the manufacturing method. Well dispersed nanofillers act as an integrated sensing network. Damage or strain severs the well-connected nanofiller network thereby causing a local change in conductivity. The self-sensing capabilities of these modified composites can be combined with low cost, minimally invasive imaging modalities such as electrical impedance tomography (EIT) for damage detection. To date, however, EIT has exclusively been used for damage detection in planar coupons. These simple plate-like structures are not representative of real-world complex geometries. This thesis advances the state of the art in conductivity-based structural health monitoring (SHM) and nondestructive evaluation (NDE) by addressing this limitation of EIT. The current study will look into damage detection of a non-planar multiply connected domain – a filament-wound glass fiber/epoxy tube modified by carbon black (CB) filler. The results show that EIT is able to detect through holes as small as 7.94 mm in a tube with length-to-diameter ratio of 132.4 mm-to-66.2 mm (aspect ratio of 2:1). Further, the sensitivity of EIT to damage improved with decreasing tube aspect ratio. EIT was also successful in detecting sub-surface damage induced by low velocity impacts. These results indicate that EIT has much greater potential for composite SHM and NDE than prevailing work limited to planar geometries suggest.</p> </div> <br>

Laser cladding is a more recent approach to repair of aviation components within a damage tolerant framework, with its ability to restore not simply the geometric shape but the static and fatigue strength as well. This research analysed the fatigue performance of Ti-6Al-4V that has undergone a laser clad repair, comparing baseline specimens with laser clad repaired, and repaired and heat treated specimens. First an understanding of the microstructure was achieved by use of BSE imagery of the substrate, clad repaired region and post heat treated regions. The substrate of the material was identified with large grains which compared to a repaired clad region with a much finer grain structure that did not change with heat treatment. Next, performance of the specimens under tensile fatigue loading was conducted, with the clad specimens experiencing unexpectedly high fatigue performance when compared to baseline samples; the post heat treated specimen lasting significantly longer than all other specimens. It is theorised that the clad may have contributed to an increase in fatigue resilience due to its fine microstructure, when compared to the softer, more coarse substrate. The heat treatment is likely to have relaxed any residual stresses in the specimens leading to a reduction in any potential undesirable stresses, without impacting the microstructure. Residual stress analysis using EDD was unproductive due to the unexpected coarse microstructure and did not provide meaningful results. Fractography using the marker-band technique was explored with some success, proving a feesable method for measuring fatigue crack growth through a specimen post failure. Unfortunately fatigue crack growth throughout the entire fatigue life was not possible due to the tortuous fracture surface and potentially due to the fine micro-structure of the clad, resulting in interrupted marker-band formation. Future research shall expand on this work with a greater focus on residual stress analysis and its impact on fatigue.

Quick and accurate predictions of equivalent properties for thin-walled composite structures are required in the preliminary design process. Existing literature provides analytical solutions to some structures but is limited to particular cases. No unified approach exists to tackle homogenization of thin-walled structures such as beams, plates, or three-dimensional structures using the thin-walled approximation. In this work, a unified approach is proposed to obtain equivalent properties for beams, plates, and three-dimensional structures for thin-walled composite structures using mechanics of structure genome. The adopted homogenization technique interprets the unit cell associated with the composite structures as an assembly of plates, and the overall strain energy density of the unit cell as a summation of the plate strain energies of these individual plates. The variational asymptotic method is then applied to drop all higher-order terms and the remaining energy is minimized with respect to the unknown fluctuating functions. This has been done by discretizing the two-dimensional unit cell into one-dimensional frame elements in a finite element description. This allows the handling of structures with different levels of complexities and internal geometry within a general framework. Comparisons have been made with other works to show the advantages which the proposed model offers over other methods.

<div>Self-sensing materials are engineered to transduce mechanical effects like deformations and damages into detectable electrical changes. As such, they have received immense research attention in areas including aerospace, civil infrastructure, robotic skin, and biomedical devices. In structural health monitoring (SHM) and nondestructive evaluation (NDE) applications, damages in the material cause breakage in the conductive filler networks, resulting in changes in the material's conductivity. Most SHM and NDE applications of self-sensing materials have used direct current (DC) measurements. DC-based methods have shown advantages with regard to sensitivity to microscale damages compared to other SHM methods. Comparatively, alternating current (AC) measurement techniques have shown potential for improvement over existent DC methods. For example, using AC in conjunction with self-sensing materials has potential for benefits such as greater data density, higher sensitivity through electrodynamics effects (e.g., coupling the material with resonant circuitry), and lower power requirements. Despite these potential advantages, AC techniques have been vastly understudied compared to DC techniques. </div><div><br></div><div>To overcome this gap in the state of the art, this thesis presents two contributions: First, an experimental study is conducted to elucidate the effect of different damage types, numbers, and sizes on AC transport in a representative self-sensing composite. And second, experimental data is used to inform a computational study on using AC methods to improve damage detection via electrical impedance tomography (EIT) – a conductivity imaging modality commonly paired with self-sensing materials for damage localization. For the first contribution, uniaxial glass fiber specimens containing 0.75 wt.% of carbon nanofiber (CNF) are induced with five types of damage (varying the number of holes, size of holes, number of notches, size of notches, and number of impacts). Impedance magnitude and phase angle were measured after each permutation of damage to study the effect of the new damage on AC transport. It was observed that permutations of hole and notch damages show clear trends of increasing impedance magnitude with the increasing damage, particularly at low frequencies. These damages had little-to-no effect on phase angle, however. Increasing numbers of impacts on the specimens did not show any discernable trend in either impedance magnitude or phase angle, except at high frequencies. This shows that different AC frequencies can be more or less useful for finding particular damage types.</div><div><br></div><div>Regarding the second contribution, AC methods were also explored to improve damage detection in self-sensing materials via EIT. More specifically, the EIT technique could benefit from developing a baseline-free (i.e., not requiring a ‘healthy’ reference) formulations enabled by frequency-difference (fd) imaging. For this, AC conductivity measurements ranging from 100 Hz to 10 MHz were collected from various weight fractions of CNF-modified glass fiber/epoxy laminates. This experimental data was used to inform fdEIT simulations. In the fdEIT simulations, damage was simulated as a simple through-hole. Simulations used 16 electrodes with four equally spaced electrodes on each side of the domain. The EIT forward problem was used to predict voltage-current response on the damaged mesh, and a fdEIT inverse problem was formulated to reconstructs the damage state on an undamaged mesh. The reconstruction images showed the simulated damage clearly. Based on this preliminary study, this research shows that fdEIT does have potential to eliminate the need for a healthy baseline in NDE applications, which can potentially help proliferate the use of this technique in practice.</div>

<p>The Mechanics of Structural Genome (MSG) is a unified homogenization theory used to find equivalent constitutive models for beam, plate, and solid structures. It has been proven accurate for periodic structures. However, for certain applications such as non-prismatic wind turbine blades and helicopter flexbeams featuring ply drop-off, where there is no repeating structure and the periodic boundary condition cannot be used, MSG's accuracy is limited. In this work, we aim to extend MSG to find element stiffness matrices directly for aperiodic structures, instead of beam properties or three-dimensional (3D) solid material properties. Two finite elements based on MSG have been developed: Heterogeneous Beam Element (HBE) and Heterogeneous Solid Element (HSE).</p> <p><br></p> <p>For beam modeling, the beam-like structure is homogenized into a series of 3-node Heterogeneous Beam Elements (HBE) with 18×18 effective beam element stiffness matrices. These matrices are used as input for one-dimensional (1D) beam analysis using the Abaqus User Element subroutine (UEL). Using the macroscopic beam analysis results as input, we can also perform dehomogenization to predict the stresses and strains in the original structure. We use three examples (a prismatic composite beam, an isotropic homogeneous tapered beam, and a composite tapered beam) to demonstrate the capability of HBE and show its advantages over the MSG cross-sectional analysis approach. HBE can capture macroscopic behavior and detailed stresses due to non-prismatic geometry.</p> <p><br></p> <p>The Heterogeneous Solid Element (HSE) is developed based on MSG to model a heterogeneous body as an equivalent solid element using an effective element stiffness matrix. HSE modeling includes homogenization, macroscopic global analysis, and dehomogenization to recover local strains/stresses. HSE avoids the local periodicity assumption for traditional multiscale modeling techniques for composite structures that compute effective material properties instead. Abaqus composite solid element and MSG-based traditional multiscale modeling are used to validate the accuracy of HSE. All example results show that HSE is more accurate in predicting global structural behavior and local strains/stresses.</p> <p><br></p> <p>HBE and HSE provide a new concept for modeling aperiodic composite structures by modeling structures into equivalent beam or solid elements instead of beam properties of the reference line in 1D beam analysis or material properties of material points in solid structural analysis.</p>

<p>Extrusion Deposition Additive Manufacturing (EDAM) is a process in which fiber-filled thermoplastic polymers pellets get molten in the extruder and deposited onto a build plate in a layer-by-layer basis. The use of short fiber composite for EDAM has enabled large-scale 3D printing structures and tools for traditional composite manufacturing processes. Successful EDAM production critically depends on the understanding of the process-structure-property relationship. Especially on the bonding between the beads which is of paramount importance in additive manufacturing since it affects primarily the fracture and strength characteristics of the printed part. Bonding is influenced mainly by the temperature history and the contact between the beads. Both of which is dependent on the fiber orientation within the bead induced by the flow deformation that occurs according to the printing parameters. This study aims to investigate and model the complex relationship between the printing conditions and inter-bead bonding in the lateral direction.</p> <p>A framework was developed to facilitate this aim, and it contains a fusion bonding model that couples the time-temperature history and the bead-to-bead contact interface. Four deposition parameters were studied: the nozzle height, ratio of the print velocity to extrudate velocity, bead-to-bead spacing, and layer time. First, a deposition flow model was developed, utilizing the anisotropic viscous flow model and smooth particle hydrodynamic finite element formulation, to predict the fiber orientation state across the deposited bead and the bead-to-bead interface for the given set of deposition parameters. Next, the effect of printing conditions on the temperature history of the bead was discovered by utilizing the heat transfer process simulation in ADDITIVE3D. Third, the experimental characterization procedure for mode I fracture toughness in the lateral direction was developed, and the fracture toughness was characterized using linear elastic fracture mechanics principles. Lastly, the phenomenological model for non-isothermal lateral fusion bonding was characterized using the bead contact interface, temperature history, and fracture toughness properties. This work showed a comprehensive effort in fusion bonding modeling while also presented a valuable process-structure-property-performance relationship in EDAM.  Guidance on the selection of printing conditions and strategy can be made using the developed model to print higher-strength parts.  </p>

<div>As the use of fiber-reinforced polymer composites grows in aerospace structures, there is an emerging need to implement damage tolerant approaches. The use of <i>in-situ</i> synchrotron X-ray tomography enables direct observations of progressive damage relative to the microstructural features, which is studied in a T650/5320 laminate composite with varying layup orientations (using 45^o and -45^o plies) in a compact tension specimen geometry. Specifically, the interactions of micromechanical damage mechanisms at the notch tip were analyzed through 3D image processing as the crack grew. First, monotonic tests were conducted where X-ray tomography was acquired incrementally between the unloaded state and maximum load. The analysis of the monotonic tension specimens showed intralaminar cracking was dominant during crack initiation, delamination became prevalent during the later stages of crack progression, and fiber breakage was, in general, largely related to intralaminar cracking. After the monotonic tension analysis, modifications were made to the specimen geometry and the loading assembly, and fatigue tests were conducted, also using <i>in-situ</i> synchrotron X-ray tomography. Specifically, tomography images were acquired after select intervals of cyclic loading to examine the crack growth behavior up to 5802 cycles. The analysis of the fatigue tests showed that intralaminar cracking was also dominant, while localized delamination allowed ply cross-over. A finite element analysis was conducted by comparing the crack profile at varying intervals of loading, and the change in stored energy per cycle, dU/dN, was calculated. The combined experimental and simulation analysis showed that when the per ply values of dU/dN were examined, the intralaminar cracking rate collapsed to one curve regardless of the ply orientation, where direct observations of fiber bridging were characterized and associated with a reduction in crack growth rate for the influenced ply. Overall, this work provides a physical understanding of the micromechanics facilitating intralaminar crack growth in composites, providing engineers the necessary assessments for slow crack growth approaches in structural composite materials.<br></div>